Sodium propionate coated with sorbitan higher fatty acid ester and process for its preparation

ABSTRACT

Non-caking sodium propionate is obtained by coating sodium propionate with a sorbitan higher fatty acid ester such as sorbitan monolaurate. The coating is performed by adding 10-500 ppm by weight of the sorbitan higher fatty acid ester to an aqueous solution of sodium propionate, removing the aqueous medium from the resultant mixture, and drying it. An organic medium may be used instead of the aqueous medium. This coating prevents sodium propionate from caking during storage.

United States Patent Ueno et al. Dec. 18, 1973 [54] SODIUM PROPIONATE COATED WITH 3.617.299 11 1971 Mattoon et al. 99/166 x SORBITAN HIGHER FATTY ACID ESTER i egura AND PROCESS FOR ITS PREPARATION 3,459,798 8/1969 Lassiter 260/537 [75] Inventors: Ryuzo Ueno, Nishinomiya; Tetsuya 3,507,665 4/1970 Henthorn.. .1 99/166 Miyazaki Shigeo Inamine 1 HySOn Nishinomiya; Saburo Kishi, Osakay 3,164,476 1/1965 Dalby et 3|. 99/92 all of Japan FOREIGN PATENTS OR APPLICATIONS [73] Assignee: Ueno Fine Chemical Industries, Ltd., 673,321 10/1963 Canada 252/385 Osaka Japan 17,573 6/1970 Japan 99/166 [22] Filed: July 1971 Primary ExaminerWilliam D. Martin [21] Appl. No.: 164,808 Assistant Examiner--Shrive P. Beck Attorney-Sherman and Shalloway [30] Foreign Application Priority Data 57 ABSTRA July 24, 1970 Japan 45/64295 CT Non-caking sodium propionate is obtained by coating [52] us. c1 117/100 A, 99/90, 99/166, sodium p p na e with a sorbitan higher fatty acid 1 17/167 ester such as sorbitan monolaurate. The coating is per- [51] Int. Cl 844d 1/00, 844d 5/08 formed y adding 10-500 ppm y e ght of the SOrbi- 581 Field of Search 117/100 A, 167; tan higher fatty acid ester to an aqueous solution of 99/224 118 163 166 90 167; 260/526, sodium propionate, removing the aqueous medium 537 R 540; 252/384 from the resultant mixture, and drying it. An organic medium may be used instead of the aqueous medium. [56] References Cit d This coating prevents sodium propionate from caking UNITED STATES PATENTS dumg Storage- 2,830,906 4/1958 Farbak et a] 99/118 R X 5 Claims, N0 Drawings SODIUM PROPIONATE COATED WITH SORBITAN HIGHER FATTY ACID ESTER AND PROCESS FOR ITS PREPARATION The invention relates to non-caking sodium propionate, and to a process for preventing the caking of sodium propionate.

Sodium propionate finds wide applications as a preservative for bread and cakes and also for animal feed. This compound is very hydroscopic and tends to cake. Even when it is sealed from the atmospheric air in an attempt to avoid moisture absorption, it cakes to form a mass under a relatively small load. Therefore, when bags of sodium propionate are stacked and stored for prolonged periods of time, the sodium propionate cakes considerably and is not easily disintegrated.

Generally, the caking of a water-sluble substance is considered to be due to the fact that on the surfaces of the particles of the substance, the cycle of dissolving the particles in moisture contained in the particles and recrystallizing them by evaporation of water is repeated, and that the transfer of substance takes place to cause the particles to adhere to one another at their contacting surfaces to form a mass. Caking, therefore, is closely related to the amount of moisture and areas of contact between the particles, and as a matter of course, proceeds markedly with an increase in the mositure content and the contacting area. In order to prevent the caking of such a substance, it is necessary to reduce the moisture content as much as possible, and minimize the contacting area.

By an ordinary drying method, sodium propionate can be dried to a moisture content of about 0.1 to 0.5 percent. However, drying costs are very high. In order to minimize the areas of contact between the particles, it is necessary to reduce the load on the particles as much as possible, but in mass production, there is a limit in doing so.

Previously, the caking of sodium propionate has been prevented for example by packing sodium propionate in units of to kilograms and placing each unit in one box so as not to exert a large load, or by coating the surfaces of the particles with a water-insoluble substance such as calcium carbonate, magnesium carbonate, calcium phosphate, or calcium stearate. The former method of avoiding a large load is based on the minimization of the areas of contact between the crystals of sodium propionate as mentioned above. However, when sodium propionate is produced in large quantities, it is difficult to pack it into boxes automatically. This requires large manpower, and the cost of packaging boxes adds to the cost of the sodium propionate, which appreciably affects the cost of production of the sodium propionate. The latter method of preventing caking of sodium propionate by a water-soluble anti-caking agent is also based on the minimization of the areas of contact between the crystals of sodium propionate. In thie prior method, the amount of anticaking agent should be as much as l to 10 percent based on the weight of sodium propionate in order to produce the intended anti-caking effect. Furthermore, according to this method, the anti-caking agent must be mixed after sodium propionate has been obtained in the form of crystals, and a procedure of thoroughly mixing them is required. In addition, the anti-caking effect is not durable, and when the anti-caking agent is added to water, turbidity is very evident.

These defects of the prior arts have now been overcome by the present invention.

In one aspect of the invention, a non-caking sodium propionate coated with a sorbitan higher fatty acid is provided.

In another aspect of the invention, a process is provided for preventing the caking of sodium propionate which comprises coating sodium propionate with the sorbitan higher fatty acid ester.

It has now been found that even a small amount of the sorbitan higher fatty acid ester can be coated in a thin film on sodium propionate, that the coating effectively prevents the crystals of sodium propionate from directly contacting one another, and that the dissolution of the crystals by moisture on their surfaces and their precipitation by evaporation of water can be reduced.

Sodium propionate, as referred to in the present invention, is in the form of crystals, powders, granules or flakes, the particle size ranging from 50 microns to 5 The sorbitan higher fatty acid ester used as a coating agent in the present invention is substantially colorless, odorless, and non-toxic, and can effectively prevent caking when used in small amounts. Examples of the sorbitan fatty acid ester are esters of sorbitan with fatty acids having 12 to 18 carbon atoms, and specifically include sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate, sorbitan tristearate, sorbitan monoleate, or sorbitan trioleate. Sorbitan monolaurate, sorbitan monooleate, and sorbitan trioleate are especially preferred as they are oily substances at room temperature. Other sorbitan fatty acid esters are waxy substances, and difficult to dissolve in an aqueous medium. But if they are added to a heated aqueous medium (for example, to C.), relatively uniform dispersing is possible, and therefore, they can also be used.

One embodiment of the process of the present invention comprises mixing an aqueous solution of sodium propionate with 10-500 ppm by weight, based on the sodium propionate, of a sorbitan higher fatty acid ester to make a uniform dispersion, removing the aqueous medium from the dispersion, and drying it to therby obtain coated sodium propionate.

Another embodiment of the process of the invention involves adding sodium propionate to a 0.1-l wt. percent (preferably 0.20.8 wt. percent) solution of a sorbitan higher fatty acid ester in an organic solvent, mixing them with each other, collecting sodium propionate by such means as filtration, removing the organic solvent, and drying the product to thereby obtain coated sodium propionate. In this embodiment, excess sorbitan higher fatty acid ester is contained in the filtrate. The filtration should be performed at reduced pressure such that 10-500 ppm by weight of the sorbitan higher fatty acid ester will remain in the sodium propionate. The removal of the excess sorbitan higher fatty acid ester may be carried out by centrifugal separation. In any case, suction filtration or centrifugal separation isstopped when an organic solvent solution of 10-500 ppm by weight, based on the sodium propionate, of the sorbitan higher fatty acid ester remains. This can be determined by measuring the ester content of the sample.

According to still another embodiment of the process of the invention, sodium propionate is added to a solution in an organic solvent of 10-500 ppm of a sorbitan higher fatty acid ester to form a slurry. Thereafter, the organic solvent is removed, and the remainder dried to recover coated sodium propionate.

In still another embodiment, an organic solvent solution of 0.5-5 wt. percent (preferably 1-3 wt. percent) sorbitan higher fatty acid ester is sprayed onto sodium propionate while the latter is being stirred so that the amount of the sorbitan higher fatty acid ester in the resulting coated sodium propionate is -500 ppm; subsequent drying gives coated sodium propionate.

Sodium propionate is generally produced by adding an aqueous solution of sodium hydroxide to an aqueous solution of propionic acid to neutralize the latter and form an aqueous solution containing 20-50 wt. percent of sodium propionate, and drying the solution to produce solid sodium propionate. When water is used as a medium in the coating of sodium propionate with a sorbitan higher fatty acid ester, a predetermined amount of a sorbitan higher fatty acid ester may be added during the manufacture of sodium propionate described to effect uniform dispersion. This simply leads to coated sodium propionate without using any particular operation. Therefore, the process utilizing water as the medium is preferred because ofits low cost of production.

On the other hand, when an organic solvent is used in the coating process, solid sodium propionate produced by the method described above should be used for the coating process since the sodium propionate is difficultly soluble in the organic solvent. This is disadvantageous from the standpoint of increased cost of production.

Examples of the organic solvent used in the process of the invention include lower alcohols such as methanol, ethanol, propanol, isopropanol, or n-butanol, benzene-type hydrocarbons such as benzene, xylene and toluene, and aliphatic hydrocarbons such as chloroform and hexane. The organic solvents that are used in the invention have a boiling point of 50 to 150C., preferably 60l20C., and can dissolve the sorbitan higher fatty acid ester of a predetermined amount and be removed by heating or spray drying. The preferred organic solvents are lower alcohols or benzene.

The removal and drying of the aqueous medium or organic medium can be effected by customary means. For example, drum drying or spray drying by heating under reduced pressure or atmospheric pressure or by heating with hot air can be utilized in the invention. By any of these methods, the drying is performed until the resulting coated sodium propionate has a moisture content of O. l-l percent by weight, preferably 0.1-0.5 percent by weight, based on the sodium propionate.

According to spray drying, crystals or powders of sodium propionate having a particle size of about 50 microns to 500 microns are coated with the sorbitan higher fatty acid ester. By the drum drying, granular sodium propionate having a particle size of 0.5 to 1 mm to flaky sodium propionate having a particle size of 0.5 to 5 mm are coated with the sorbitan fatty acid ester. Of course, sodium propionate can be made into fine crystals (3-50 microns). Because of their small size, however, such fine crystals especially tend to scatter off and absorb moisture to a great extent, and are not commercially feasible. Gathering of the fine crystals will result in powders (SO-500 microns), granules (0.5 to 1 mm), or flakes (0.5 to 5 mm).

The amount of sodium propionate to be added to the aqueous solution in the first-mentioned embodiment is 10 to percent by weight, preferably 20 to 50 percent by weight. If sodium propionate is dissolved in hot water to prepare an aqueous solution, the concentration of it in the aqueous solution is usually about 60 percent by weight, but the preferred concentration is 20 to 50 percent by weight.

The amount of the sorbitan higher fatty acid ester coated as the anti-caking agent is 10 to 500 ppm by weight, preferably 30 to 300 ppm by weight based on the weight of sodium propionate. If the amount is less than 10 ppm by weight, the anti-caking effect is insufficient, and amounts around 200 ppm are most effective. Amounts larger than 500 ppm by weight result in a descreased anti-caking effect, and the increased amounts of the sorbitan higher fatty acid ester adversely affect the quality of the sodium propionate. The reason is considered to be that the increased amounts of the sorbitan higher fatty acid ester cause the wetting of the crystals of sodium propionate.

The sorbitan higher fatty acid esters used in the process of the invention as an anti-caking agent are colorless, odorless, and non-toxic, and are suitable for use in coating sodium propionate which is a preservative for fooodstuffs. A marked anti-caking effect is exhibited by using as small an amount as l0-500 ppm by weight of this sorbitan ester on the basis of the sodium propionate. Such small amounts do not affect the efficacy of sodium propionate, nor cause marked reduction in purity. The product of the present invention retains its transparency even when dissolved in water, and hardly differs from uncoated sodium propionate. The anticaking effect attained by the present invention is also excellent in that even in the source of long periods of time under a load, the effect is hardly lost.

The following Examples are presented to illustrate the invention, and are not intended in any way to limit the invention. In the Examples, all parts and percentages are by weight.

EXAMPLE 1 A dispersion of each of the sorbitan fatty acid esters indicated in Table l in 10 times their weight of water was added to a 40 percent aqueous solution of sodium propionate in the concentrations indicated in Table l. The resultant mixture was spray dried to form powders of sodium propionate having a moisture content of 0. l 5 to 0.2 percent.

The degree of caking of the powders of sodium propionate obtained was measured by the following method. Eight grams of the sample were packed into a cylinder having a diameter of 3 cm and a height of 4 cm, and a pressure of l kg/cmG was applied to the sample at 37C. and a relative humidity of 50 percent to shape the sample for one hour. The load needed to destroy the shaped article was determined. On the other hand, sodium propionate containing no anti-caking agent was shaped, and the load needed to destroy the shaped article was determined. The break load for the shaped article of sodium propionate containing no anti-caking agent was defined as l, and the degree of caking was defined as a ratio of the break load for the shaped article of sodium propionate containing anti-caking agent against the break load for the shaped article containing no anti-caking agent. The results are given in Table l.

TABLE 1 Anti-caking Amount Break load Degree of agent (ppm) (kg/cm) caking Not added 0.89 l Sorbitan 5 0.83 0.93

monolaurate v 0.78 0.88 30 0.68 0.76 50 0.58 0.65 100 0.29 0.33 200 0 0 300 0.16 0.18 500 0.67 0.75 Sorbitan monooleate 5 0.85 0.95 10 0.80 0.90 30 0.74 0.83 50 0.69 0.78 200 0.34 0.39 300 0.38 0.43 500 0.55 0.62 Sorbitan trioleate 5 0.8 l 0.91 10 0.76 0.85 30 0.70 0.79 200 0.37 0.42 300 0.33 0.37 500 0.36 0.40

The break load of 0 in the table indicates that there was hardly any caking, and the product lost its shape upon withdrawal from the vessel.

EXAMPLE 2 One thousand kilograms of a 40 percent aqueous solution containing 400 kg of sodium propionate were mixed with 200 g of a dispersion of 20 g of sorbitan monolaurate in 180 g of water, and the mixture was uniformly stirred. The mixture was drum dried to form flaky sodium propionate having a moisture content of 0.1 percent.

kg of the flaky sodium propionate were packed into a bag composed of polyethylene film having a thickness of 0.6 mm inside and three layers of kraft paper outside, and sealed up. Four such bags were placed flat (contact areas 1600 to 1800 cm), and a pressure of 11 00 kg was applied thereto. In this state, the bags were left for one month at 25C.

Sodium propionate in flaky form (moisture content 0.1 percent) containing no anti-caking agent was prepared, and the same caking test as above was performed. The results are given in Table 2.

TABLE 2 State of caking Large concrete-like mass was formed Soft caked state, but readily disintegrated into the original flakes Anti-caking agent Not added Sorbitan monolaurate EXAMPLE 3 spray dried to a moisture content of O. l 5 to 0.2 percent' to form powders of sodium propionate.

The degree of caking of the resulting coated sodium propionate was determined in the same way as described in Example 1, and the results are given in Table TABLE 3 Anti-caking Amount Break load Degree of agent (ppm) (kg/cm) caking not added 0 0.85 l 10 0.82 0.96 50 0.65 0.76

Sorbitan monopalmitate 200 0.20 0.24 300 0.30 0.35 500 0.73 0.86 10 0.84 0.99 50 0.69 0.81

Sorbitan monostearate 200 0.32 0.38 300 0.36 0.42 500 0.72 0.85 10 0.85 l 50 0.71 0.84 200 0.34 0.40

Sorbitan tristearate 300 0.37 0.44 500 0.71 0.84

EXAMPLE 4 600 Grams of sorbitan monooleate were added to 30 kg of benzene, and a solution was prepared by heating to 45C.. Ten kilograms of flaky sodium propionate (moisture content 0.2 percent by weight) having a particle diameter of 1 3 mm were added, and mixed for 30 minutes while stirring the solution so that the surface of sodium propionate was thoroughly wetted with the benzene solution. The mixture was then subjected to suction filtration so that the sodium propionate contained 4 percent by weight of the benzene solution. Sodium propionate was taken out, and benzene was completely evaporated in hot air at C., followed by drying. Coated sodium propionate containing 400 ppm of sorbitan monooleate was obtained.

EXAMPLE 5 Powders of sodium propionate having a particle size of 200 to 500 microns (10 kg) were put into a coating pan. While rotating the pan, 30 g of an iso-propyl alcohol solution at 45C. containing 2 percent by weight of sorbitan monolaurate were sprayed onto the surface of sodium propionate. Thereafter, by blowing hot air at 70C., isopropyl alcohol was evaporated. This cycle of spraying and hot air blowing was repeated five times, and a total of g of the iso-propyl alcohol solution was sprayed so that the amount of sorbitan monolaurate in the coated sodium propionate was 300 ppm. Sodium propionate coated with sorbitan monolaurate was obtained.

EXAMPLE 6 Three grams of sorbitan monopalmitate were added to 20 kg of methanol, and a complete solution was prepared by heating to 45C. 10 kg of sodium propionate having a particle diameter of 200 to 500 microns were added, and with slow stirring, a uniform slurry was prepared. Methanol was evaporated by a drum dryer, followed by drying. Sodium propionate coated with 300 ppm of sorbitan monopalmitate was obtained.

What we claim is:

l. Non-caking sodium propionate having a particle diameter of 50 microns to 5 mm coated with a sorbitan higher fatty acid ester in an amount of 10 to 500 ppm by weight based on the weight of the sodium propionate.

2. The non-caking sodium propionate of claim I wherein said sorbitan higher fatty acid ester is an ester wherein said sorbitan higher fatty acid ester is selected from the group consisting of sorbitan monolaurate, sor bitan monooleate and sorbitan trioleate.

5. The non-caking sodium propionate of claim 1 wherein the amount of said sorbitan higher fatty acid ester is 30 to 300 ppm based on the weight of the sodium propionate. 

2. The non-caking sodium propionate of claim 1 wherein said sorbitan higher fatty acid ester is an ester of sorbitan with a fatty acid having 12 to 18 carbon atoms, said ester being substantially colorless, odorless and non-toxic.
 3. The non-caking sodium propionate of claim 1 wherein said sorbitan higher fatty acid ester is selected from the group consisting of sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate, sorbitan tristearate, sorbitan monooleate, and sorbitan trioleate.
 4. The non-caking sodium propionate of claim 1 wherein said sorbitan higher fatty acid ester is selected from the group consisting of sorbitan monolaurate, sorbitan monooleate and sorbitan trioleate.
 5. The non-caking sodium propionate of claim 1 wherein the amount of said sorbitan higher fatty acid ester is 30 to 300 ppm based on the weight of the sodium propionate. 